As wireless communication networks evolve, prevalence of Machine-Type Communication (MTC), from MTC devices in wireless communications networks, is likely to expand due to an expected rise in numbers of MTC devices deployed in these networks, in applications such as smart electricity metering, which are transmitting and receiving data in the networks.
Accordingly, methods of controlling network access have been designed, and in some cases implemented, for Machine-Type Communication (MTC) devices in wireless communication networks. An existing example of a method of controlling MTC device access to a wireless communication network utilises the random access channel (RACH) of the network to provide contention-based access to wireless terminals, such as the MTC device, in the network to request connection setup when no radio resource has been allocated to the wireless terminal. For example, in networks based on the Long Term Evolution (LTE) standard (e.g. Release11 LTE), a wireless terminal sends an access request message to an eNodeB in a network on the RACH (Random Access Channel). This access request message includes a random access preamble, which is selected by the wireless terminal, from two subsets of available preamble sequences (Random Access Resource). The selection of the subset of preamble sequence is determined by the optimum amount of data, as well as power, that the wireless terminal intends to transmit on the uplink transport channel (UL-SCH). Upon the detection of the random access request message, the eNodeB may either accept or deny the access request. If it accepts an access request, the eNodeB transmits a random access response message on the downlink transport channel (DL-SCH) to the wireless terminal including information such as the detected index of the random access preamble sequences, timing correction, scheduling grant, and a Temporary Cell—Radio Network Temporary Identifier (TC-RNTI). Also, the wireless terminals monitor L1/L2 control channels within a network-controlled configurable time window for the random access response from the network.
It will be appreciated by those persons skilled in the art that contention occurs when two or more wireless terminals perform simultaneous random-access attempts using the same preamble sequences. In the event of such a contention, those wireless terminals will listen to the same random access response message on the DL-SCH and therefore have the same Temporary Cell—Radio Network Temporary Identity (TC-RNTI). In this case, multiple wireless terminals will react to the same downlink response message and a collision will occur. In the event of a contention, the eNodeB will resolve the contention in favour of one of the wireless terminals. The failed random access procedure wireless terminals will then “back-off” and perform new access requests at calculated later times. However, as the number of wireless terminals in a network increases with the rise in prevalence of MTC devices, there is a greater probability of contention and a greater number of access attempts will fail. If too many contentions occur, throughput on RACH will be significantly reduced.
As discussed, the anticipated introduction of LTE based low cost Machine Type Communication (MTC) devices, which are expected to be deployed in a specific area, will greatly increase the problem of radio network congestion and signalling network congestion. Additionally, the increasing number of contentions will require the MTC devices to work harder and hence consume more power.
There are several existing solutions that have been proposed to address this problem of radio network congestion. These include:
1. Access Class Barring
2. Separate RACH resources for MTC
3. Dynamic allocation of RACH Resources
4. MTC specific back off scheme
5. Slotted access
6. Pull based scheme.